There are many medical procedures where a surgeon needs to attach soft tissue to bone. The soft tissue can be tendon or other connective tissue. One very common example of this is rotator cuff repair where a portion or all of the rotator cuff is torn or detached from the humerus. When the rotator cuff tears from the humerus, the result is pain and loss of function. Rotator cuff disease affects a large number of people worldwide, affecting many people over the age of forty. Some studies have shown a prevalence of approximately 30% in people over the age of forty (Rockwood C., et al., The Shoulder, Saunders, 2004; 820-821). It is estimated that as many as 17 million people in the United States may be at risk for pain and dysfunction as a result of rotator cuff injuries. While the majority of people are asymptomatic, a significant subset goes on to have disability. One study in patients with rotator cuff tears in one shoulder found that 50% of these patients who had an asymptomatic rotator cuff tear in the other shoulder went on to become symptomatic (Yamaguchi, K., et al., J. Shoulder Elbow Surg., 2001;10:199-203).
The prevalence of symptomatic rotator cuff disease is reflected in the large numbers of surgical repair for this condition. Rotator cuff repair is one of the most common orthopedic procedures performed. When a patient presents with a significant rotator cuff tear, surgical repair is performed. The goal of surgical repair of the rotator cuff is to secure the tendon to the bone in a stabile manner so that the tendon can reattach to the bone and can heal. If the tendon is not stabile and oscillation or micro-motion between the tendon and bone develops, the healing process will be interrupted. In this situation, it is less likely that the tendon will heal properly to the bone, resulting in a re-tear. Thus, the more stabile the repair, the more successfully the tendon will heal to the bone.
Rotator cuff repair is performed open or arthroscopically, most often using suture anchors. These have one point of fixation with either one suture or several sutures attached for reattaching the tendon to the bone. While arthroscopic repair is less painful and thus more attractive to patients, many surgeons continue to perform open rotator cuff repairs. Much of the reason for this is due to the challenge of arthroscopic shoulder surgery. There is a significant learning curve in gaining the skills to be able to manage multiple strands of suture in a relatively small field of view, passing these through the tendon and knotting the sutures in the process of tying the tendon into apposition with the bone. Many of these techniques can be relatively time-consuming when compared with open surgery.
There is a growing body of literature showing that surgical rotator cuff repair has a high rate of failure. Failure of rotator cuff repairs is a well-described complication of rotator cuff repairs, both open and arthroscopic. For example, Gerber et al. found a re-tear rate of 20% following isolated repair of the supraspinatus. Bishop found a re-tear rate of 31% in arthroscopic and 47% in patients undergoing open repair (Bishop J., et al. Cuff integrity after arthroscopic versus open rotator cuff repair: A prospective study, J. Shoulder Elbow Surg., 2006;15:290-299). Galatz found an even higher re-tear rate in larger tears (Galatz, L., et al., The outcome and repair integrity of completely arthroscopically repaired large and massive rotator cuff tears, J. Bone Joint Surg. Am., 2004;86A:219-24). Tendon-to-bone reattachment in a rotator cuff repair procedure can fail by a number of means. In a review of failed rotator cuff surgeries evaluated at re-operation, Cummins cited as one of the weak links in the repair, the suture-tendon interface (Cumins, C. A., et al., Mode of failure for rotator cuff repair with suture anchors identified at revision surgery, J. Shoulder Elbow Surg., 2003 March-April;12(2):128-33). To reduce the load on any one suture, (i.e., greater distribution of loads) suture anchors used in tendon repair have begun to add multiple sutures to each suture anchor. Burkhart illustrates that the load on each suture diminishes as the number of sutures holding the tendon in place increases (Burkhart, S. S., et al., A stepwise approach to arthroscopic rotator cuff repair based on biomechanical principles, Arthroscopy, 2000 January-February; 16 (1):82-90). Kim demonstrated less strain and greater tendon-bone stability in repairs made with multi row (4 fixation points) than with single row (2 fixation points). However, even in the repairs made with 4 fixation points, slippage (oscillation and micro-motion) between the tendon and bone was greater than 3.0 mm after just 200 cycles of physiological loading (Kim, D., et al., Biomechanical comparison of a single-row versus double row suture anchor technique for rotator cuff repair, Am. J. Sports Med., 2006; 34;407).
FIG. 1 illustrates a common prior art configuration for attaching tendon to bone. A suture anchor 102 with a pre-attached suture 105 is first driven into the cortical shell 100 and then the cancellous portion 101 of the bone 110, after which one or both of the ends of the suture line 105 are threaded through the tendon 103. The two ends of the suture line 105 are then connected with any one of a variety of knot types 111 to bring the tendon 103 in direct contact, or apposition, with the bone 110. In tendon repair, it is a common practice to mechanically abrade or shave the cortical shell 100 to achieve a bleeding surface. It is believed that a bleeding surface will promote more rapid healing of the tendon to the bone. Stabile apposition between the tendon and bone will promote healing while micro-motion or oscillation between the tendon and the bone may disrupt the healing of the tendon to the bone. In current tendon repair techniques, stability between the tendon and the bone largely comes from the compression the suture can apply between the tendon and bone.
The objective with tendon repair is for the connection between the tendon 103 and bone 110 to remain stabile when physiological lateral force F 108 is applied. FIG. 2 depicts how a position gap 104 may form when physiological lateral force F 108 is applied to the tendon 103 when only sutures are used to apply downward compressive force to secure the tendon to the bone. As the force F 108 exceeds the frictional forces between the tendon and bone and that applied by the suture, the tendon slips along the interface between the tendon and the bone and causes the flexible, non-rigid suture 105 to further compress the tendon and rotate in the direction of the applied force F until a new force equilibrium is achieved. Thus, the undesired oscillation that results in position gap 104 is formed. Such a gap interferes with the healing of the tendon to the bone and may compromise the repair process to an extent that it becomes unsuccessful. Such force F 108 may be applied by the patient using his or her humerous before full reattachment and healing of the tendon 103 to the bone 110 has occurred.
In facilitating or augmenting tendon to bone fixation in surgical rotator cuff repair, typically sutures are passed through the torn tendon a distance medially to the tear that will be sufficient to provide enough tendon to cover the greater tuberosity of the humeral bone. Tension is then applied to the sutures to pull the tendon laterally over the area of the greater tuberosity, and mattress style knots are tied in the sutures gripping the tendon to appose the tendon to the humeral bone. The ends of the sutures are then stretched laterally over the tendon, stabilizing it to the greater tuberosity, and with a knotless anchor, fixed and tensioned to the bone at a position lateral to the tear. As force F is applied to the tendon, the lateral fixation points will stabilize the mattress knots resulting in less gap as shown in FIG. 2. However, due to limitations in their design, current knotless anchors used for lateral fixation do not always adequately fix and tension the suture to the bone or are overly complicated to use, resulting in the potential for inadequate lateral fixation, possibly resulting in the formation of the gap shown in FIG. 2.
Thus what is needed is a tendon to bone fixation method and device that will reliably and simply enhance the stability of the tendon to bone interface which in turn will minimize gap formation and tendon/bone micro-motion and provide a greater opportunity for the tendon to reattach to the bone to heal properly.